(Adding details of election candidate being killed, update death toll, context from previous attack on campaign rally earlier this week)

By Gul Yousafzai

QUETTA, Pakistan, July 13 (Reuters) - A suicide bomber hit a campaign event in southwestern Pakistan, a police official said, killing 27 people in the second election-related attack on Friday amid tensions over ousted prime minister Nawaz Sharif’s return ahead of the July 25 vote.

Among those killed was Baluchistan provincial assembly candidate Siraj Raisani, whose brother Nawab Aslam Raisani had served as the provincial chief minister from 2008 to 2013.

“My brother Siraj Raisani has been martyred,” said Haji Lashkari Raisani, another brother who is also contesting a national assembly seat from Baluchistan.

Raisani is the second electoral candidate to be killed in pre-election violence this week.

Senior police official Qaim Lashari told Reuters the bomber attacked a campaign meeting where Raisani was due to speak killing 27 and wounding over 39.

Police had earlier said that the attack targeted Raisani’s convoy but later changed their statement as video footage of a large tent showing damage from the blast was circulated.

Pakistan’s caretaker government launched a crackdown on political gatherings on Friday as Sharif, who was ousted by the Supreme Court last year and convicted in absentia of corruption a week ago, was flying back to rally his party ahead of the general elections.

Earlier in the day, a bomb blast killed four people in the northern town of Bannu when it struck the campaign convoy of Akram Khan Durrani, an ally of Sharif’s party from the religious Muttahida Majlis-e-Amal party (MMA).

A suicide bomber blew himself up at a rally by an anti-Taliban political party in the northern city of Peshawar on Tuesday, killing 20 people including Haroon Bilour who was hoping to win a provincial assembly seat in July.

The Pakistani Taliban claimed responsibility for the attack.

Bilour was part of the predominantly secular, ethnic Pashtun nationalist Awami National Party, which has long competed with Islamist parties for votes in Pakistan’s volatile Pashtun lands, along the border with Afghanistan.

His father, senior ANP leader Bashir Bilour, was killed in a suicide bombing in late 2012, in the run-up to Pakistan’s last election. (Additional reporting by Jibran Ahmad in Peshawar; Writing by Kay Johnson; Editing by Toby Chopra)